How to implement BitSet with Go?

Question

I didn't find a BitSet package in Go, so I tried to implement it. I'd like to use a array of uint64 to store the bits.

I need the number of bits to allocate the uint64 array. With Java, I can define a constructor that takes an integer. While Go doesn't provide constructor, how can I properly initialize the BitSet 'object' when user call new()?

Answer 1

The short answer is, you can't properly initialize the BitSet object when a user calls new().

The idiomatic way to do this is to create a function that returns a new BitSet object. For example, look at the list package. To create a new List, you'd call list.New() and that call would return a new List object. Because there are unexported fields in the list structure, there's not much use in creating a List with new(), as you'd be unable to initialize some fields.

Answer 2

Declare bitSet as a private struct:

type bitSet struct {
  len int
  array []uint64
}

Expose the interface BitSet:

type BitSet interface {
  Has(pos int) bool
  Add(pos int) bool
  Len() int
}

Also expose a function NewBitSet:

func NewBitSet(len int) BitSet {
  return &bitSet{len, make(uint64, (len+7) / 8) }
}

This is a Go way for encapsulation: share an interface, not the implementation.